The discovery by a local IT industry worker was made by mistake.
Apart from being the result of poor security, it may also have been aided by a side-effect of the Google search engine, in which the pages of defunct web sites containing sensitive directories remain cached and available to anyone.
The cached data, viewed by iTnews, includes 22,000 credit card numbers, including CVVs, expiry dates, names and addresses.
Up to 19,000 of these numbers could be active. Most are customers in the US and Britain although some are Australian.
The credit card numbers are for accounts held with Visa, Mastercard, American Express, Solo, Switch, Delta and Maestro/Cirrus.
Within the address bars of the cached pages are URLs of companies, including UK retailers of laboratory supplies, sports and health goods, apparel, photo imaging and clothing.
"I received a Google Alert for a name," said the worker who discovered the problem, speaking on condition of anonymity to iTnews.
"The alert started with a bunch of other numbers, so I went to the web page and it was just a virtual directory listing with a bunch of directories underneath and a load of files inside."
"It looks like the site might have been a payment processing gateway that handled credit card transactions for a bunch of websites before it went belly-up," the worker speculated.
The worker tried to report the find immediately to Visa and Mastercard, which have the lion's share of card numbers, but said neither returned calls.
iTnews has contacted the credit card providers for comment.
"We're investigating this report as a matter of priority, but it's too early to make any further comment," said a spokesperson for Visa.
The information will be handed to police tonight, the worker said.
Processing registration... Please wait.
This process can take up to a minute to complete.
A confirmation email has been sent to your email address - SUPPLIED GOES EMAIL HERE. Please click on the link in the email to verify your email address. You need to verify your email before you can start posting.
If you do not receive your confirmation email within the next few minutes, it may be because the email has been captured by a junk mail filter. Please ensure you add the domain @itnews.com.au to your white-listed senders.